1. Field of the Invention
The present invention relates to a method for generating pluripotent stem cells, a method of autologous cell transplantation with a human being, and to pluripotent stem cells generated from human testis.
2. Related Prior Art
Stem cells are cells found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialized cell types. As stem cells can be grown and transformed into specialized cells with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture, their use in medical therapies has been proposed. In particular, embryonic cell lines, autologous embryonic stem cells generated through therapeutic cloning, and highly plastic adult stem cells from the umbilical cord blood or bone marrow are touted as promising candidates.
The ability to derive pluripotent stem cells from the adult human testis has important implications for biotechnology and regenerative medicine. Although these cells are unipotently restricted to the generation of gametes in the course of normal development2,3, several lines of evidence suggest that under certain circumstances, cells of the germ line have the ability to give rise to cells that are pluripotent4-6. The term of pluripotency is differently defined in research with mouse and human stem cells. The NIH and the ISSCR guidelines and criteria for human pluripotency include teratoma formation in addition to microarray assays for transcription factors and other gene activity associated with pluripotency. Teratomas, which are tumors containing different kinds of cells and tissues from all three germ layers at various stages of maturation, occur almost exclusively in the gonads7. Furthermore, primordial germ cells (PGCs) give rise to pluripotent cells when cultured under appropriate conditions4,8. PGCs have differentiation properties similar to those of embryonic stem (ES) cells isolated from the inner cell mass9. Recently the successful establishment of germline stem cells from neonatal mouse testis was reported5. In addition, one study6 successfully generated mouse adult germline stem cells (GSCs) with pluripotency from spermatogonial stem cells from adult mouse testis. As in the experiments reported previously5, these cells were able to differentiate into derivatives of all germ layers in vitro, generated teratomas in immunodeficient mice and, when injected into an early blastocyst, contributed to the development of various organs. Similar results with GPR125+ germline progenitor cells have been reported by another study10.
Since there are considerable differences between stem cells from mice and human stem cells9 the pluripotent stem cells of mice as generated by Guan et al.6 are limited in their clinical applications in human. Therefore, there is an ongoing need to provide a reliable method for generating human adult pluripotent stem cells which can be used in clinical applications, e.g. stem cell therapies, autologous transplantations etc.